A detailed knowledge of the processes involved during the determination of the primordial germ cells is needed before a comprehensive understanding of cell determination of this specific cell type can be obtained. Our principal goals have been to clarify the normal development of pole cells in Drosophila and then to elucidate the defects which appear in mutations affecting gastrulation, and finally some specific processes of oogenesis. In specific, we will complete the analysis of the fate of 3H-thymidine labelled pole cells, transplanted into unlabelled embryos. We will continue our analysis of the maternal effect lethal mutation, 573, which affects mesoderm formation during gastrulation. Finally, we will determine the characteristics of the in vitro synthesized vitellogenins and compare them to vitellogenins isolated from fly abdomens. We will attempt to identify recombinant DNA molecules containing the vitellogenin genes. By in situ hydridization we will determine the cytogenetic locus of the genes.